Cloud Detection Capabilities over the Polar Regions from MISR

Historically, cloud detection through satellite remote sensing has been difficult over the polar regions. Clouds near the surface are especially difficult to detect, since their temperature and reflectivity are similar to the surface. The Multi-angle Imaging SpectroRadiometer (MISR), on-board the EOS-Terra platform, has the capability to detect these and other clouds using novel techniques unavailable to other satellite instruments. These novel techniques take advantage of MISR's multiple cameras, which provide images of each scene from nine viewing directions. These cameras can be combined into an animation to observe the parallax between clouds and the underlying surface. Even more striking is the use of the Band-Differenced Angular Signature (BDAS), which capitalizes on the forward-scattering properties of clouds compared to the surface. The BDAS is simply the reflectance difference between the blue and near-IR MISR channels examined as a function of view angle for those cameras viewing forward-scattered radiation. Even the thin low-level clouds that frequently occur during the spring ice breakup are easy to detect using the BDAS technique.

While these techniques have not yet been automated for global cloud detection, manual analysis of hundreds of scenes shows them to be promising. Multiple examples of the BDAS technique and animations of the multiple MISR cameras will be presented, highlighting their potential for cloud detection.